High Pass Filter (HPF) and Low Pass Filter (LPF) Mega Thread

#2,441
beans-on-toast said:
I wouldn’t think that it could with a Barefaced Super Twin 212. You’d have to ask a researcher who studies human brain wave reaction to audio to explain it. Some fortunate ones can detect frequencies beyond our hearing capabilities.

I wish I had golden ears.:laugh:
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I have golden years...doesn't count for much without hearing aides though ;):bag::headphone:...
 
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#2,442
byacey said:
Just because there is some extended high frequency content way up high in the signal, it may or may not be desirable, depending on the genre of music and style of playing. I think those upper harmonics past 8kHz would be pretty weak with anything less than brand new round wound strings and being played with a pick.
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Correct, it depends on a lot of factors.
 
#2,444
What issues are possible when chaining HPFs? Specifically, I'm trying to understand what to watch for when using an Fdeck HPF-Pre Series 3 Mini placed in the chain just before a Cali76 Compact Bass compressor, which includes a side-chain variable HPF (20-350Hz). It seems like the Fdeck might be redundant except in cases when the compressor is turned off? Would it be better to leave the Cali HPF turned off? Any tips on balancing the use of both HPFs? Seems like there's always something to wonder about!
 
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#2,445
I asked this question of Perplexity.ai, which is one of the better generative AI services but have no idea what info here is true or not. For your entertainment:

Using an external High Pass Filter (HPF) in conjunction with the built-in HPF of the Cali76 Compact Bass compressor pedal can have both advantages and disadvantages. Let's explore the pros and cons:

Pros:
  1. Greater control over low-end frequencies: Using both filters allows for more precise shaping of the bass frequencies, giving you finer control over your tone.
  2. Reduced "steamroller effect": The combination of filters can further prevent excessive compression of low frequencies, preserving more of your playing dynamics and articulation.
  3. Flexibility in signal chain: An external HPF can be placed before or after the compressor, allowing for different tonal options and compression characteristics.
  4. Potential noise reduction: Using an external HPF before the compressor can help reduce unwanted low-frequency noise or rumble before it reaches the compressor's input.
Cons:
  1. Potential loss of low-end: Excessive use of HPFs may result in a thin or weak bass tone if not carefully balanced.
  2. Increased complexity: Adding another device to your signal chain can make your setup more complicated and potentially introduce more points of failure.
  3. Redundancy: The Cali76 Compact Bass already has a well-implemented HPF, so an external one might be unnecessary in many cases.
  4. Possible phase issues: Using multiple filters could potentially introduce phase problems, especially if they are set to similar frequencies.
  5. Additional cost and pedalboard space: An external HPF means investing in another pedal and allocating space on your pedalboard.
It's important to note that the Cali76 Compact Bass's built-in HPF is specifically designed to work with its compression circuit. It filters bass frequencies out of the sidechain, allowing the compressor to react more to your playing dynamics rather than the constant low-end information. This feature is already quite effective, making an external HPF potentially redundant for many users.

If you do decide to use an external HPF, it's crucial to experiment with its placement in your signal chain and carefully adjust both filters to achieve the desired tone without compromising your bass sound's fullness and character.
 
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#2,447
agedhorse said:
The side chain HPF is not in the main signal path and only affects the control voltage to the VCA control.
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Understood. However, if the external HPF removes troublesome low frequencies in general, aren't those frequencies then removed from the signal before they even hit the compressor's side chain HPF? Seems redundant.
 
#2,449
Recently expanded my horizons with a Cali76CB. The most surprising discovery was how much the Cali's HPF enhances tone even though it's preceded by the Fdeck HPF-Pre Series 3 Mini. Both provide significant benefits. When tracking the bass, I prefer to omit the three small pedals and route the bass straight into the Noble (no EQ) and handle processing in the DAW. The extra space between the Noble and Cali facilitates easy cable plug access.

Noble-Cali76CB-HPFpre-TurboTuner-sm.JPG
 
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#2,451
I hesitate between:
Pro FDeck:
  • I don't need a footswitch (it will be always on)
  • I don't plan to use it with guitar, so the frequency range (35 to 140 Hz) is more usable than 25 to 400 hz
  • The builder is a TB member
Pro Sine Effect H24:
  • Maybe -24 dB at desired frequency is more efficient that -12 dB at 35 hz + -12 dB at disered frequency? I have no clue!
  • I prefer to buy as local as possible. Being French, Pro Sine (UK) is more local to me
I'm sure that both would be great actually, but I'd like to have your opinion…

Thoughts?
 
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#2,452
gtirard said:
I hesitate between:
Pro FDeck:
  • I don't need a footswitch (it will be always on)
  • I don't plan to use it with guitar, so the frequency range (35 to 140 Hz) is more usable than 25 to 400 hz
  • The builder is a TB member
Pro Sine Effect H24:
  • Maybe -24 dB at desired frequency is more efficient that -12 dB at 35 hz + -12 dB at desired frequency? I have no clue!
  • I prefer to buy as local as possible. Being French, Pro Sine (UK) is more local to me
I'm sure that both would be great actually, but I'd like to have your opinion…

Thoughts?
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I've tried many many different HPF formats, both analog and digital, commercial ones and my own DIY designs. For BG and acoustic guitar stage amplification I've come to prefer the 12dB/12dB format (second order/second order), or my own hybrid slope tweak which is even more interactive with the bass shelving control. For PA or recording duty I often tend to prefer a straight up 4th order (24dB/octave) format, for whatever that's worth.

As always, I have nothing to sell but do freely share many open source designs with DIY builders. In that context, a 4th order analog filter typically wants a four section log pot with closely matched sections, 12+ 12 only needs two well matched sections since one side is fixed , and my designs only need a standard one section pot with tolerance being relatively unimportant.
 
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